84 lines
2.2 KiB
C
84 lines
2.2 KiB
C
/* origin: FreeBSD /usr/src/lib/msun/src/e_atan2f.c */
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/*
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* Conversion to float by Ian Lance Taylor, Cygnus Support, ian@cygnus.com.
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*/
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/*
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* ====================================================
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* Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
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*
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* Developed at SunPro, a Sun Microsystems, Inc. business.
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* Permission to use, copy, modify, and distribute this
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* software is freely granted, provided that this notice
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* is preserved.
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* ====================================================
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*/
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#include "libc/math/libm.h"
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static const float
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pi = 3.1415927410e+00, /* 0x40490fdb */
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pi_lo = -8.7422776573e-08; /* 0xb3bbbd2e */
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float atan2f(float y, float x)
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{
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float z;
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uint32_t m,ix,iy;
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if (isnan(x) || isnan(y))
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return x+y;
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GET_FLOAT_WORD(ix, x);
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GET_FLOAT_WORD(iy, y);
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if (ix == 0x3f800000) /* x=1.0 */
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return atanf(y);
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m = ((iy>>31)&1) | ((ix>>30)&2); /* 2*sign(x)+sign(y) */
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ix &= 0x7fffffff;
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iy &= 0x7fffffff;
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/* when y = 0 */
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if (iy == 0) {
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switch (m) {
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case 0:
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case 1: return y; /* atan(+-0,+anything)=+-0 */
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case 2: return pi; /* atan(+0,-anything) = pi */
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case 3: return -pi; /* atan(-0,-anything) =-pi */
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}
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}
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/* when x = 0 */
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if (ix == 0)
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return m&1 ? -pi/2 : pi/2;
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/* when x is INF */
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if (ix == 0x7f800000) {
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if (iy == 0x7f800000) {
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switch (m) {
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case 0: return pi/4; /* atan(+INF,+INF) */
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case 1: return -pi/4; /* atan(-INF,+INF) */
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case 2: return 3*pi/4; /*atan(+INF,-INF)*/
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case 3: return -3*pi/4; /*atan(-INF,-INF)*/
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}
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} else {
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switch (m) {
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case 0: return 0.0f; /* atan(+...,+INF) */
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case 1: return -0.0f; /* atan(-...,+INF) */
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case 2: return pi; /* atan(+...,-INF) */
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case 3: return -pi; /* atan(-...,-INF) */
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}
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}
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}
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/* |y/x| > 0x1p26 */
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if (ix+(26<<23) < iy || iy == 0x7f800000)
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return m&1 ? -pi/2 : pi/2;
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/* z = atan(|y/x|) with correct underflow */
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if ((m&2) && iy+(26<<23) < ix) /*|y/x| < 0x1p-26, x < 0 */
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z = 0.0;
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else
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z = atanf(fabsf(y/x));
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switch (m) {
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case 0: return z; /* atan(+,+) */
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case 1: return -z; /* atan(-,+) */
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case 2: return pi - (z-pi_lo); /* atan(+,-) */
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default: /* case 3 */
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return (z-pi_lo) - pi; /* atan(-,-) */
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}
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}
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